Apparatus for entrenching submerged elongate structures

ABSTRACT

An apparatus for entrenching submerged elongated structures such as pipelines and the like, including a skid frame having port and starboard pontoon runners with a box frame operable to bridge the pontoon runners over a pipeline to be entrenched. The box frame includes a first and second set of upper and lower pontoon spanning supports. Each of the supports includes inwardly facing port and starboard guide rails. Vertically and horizontally adjustable port and starboard cutter and eductor heads are ruggedly supported from the box frame guide rails and extend in close proximity to the surfaces of a pipeline to be entrenched. The port and starboard cutter and eductor heads both have a generally vertical-slant-vertical configuration so that the cutter and eductor heads extend along the lateral surfaces of the pipeline, slope beneath the pipeline and extend vertically beneath the pipeline. The head configuration enables the apparatus to rapidly and efficiently cut a trench having generally vertical side walls within the bed of the body of water and educt the loosened soil or detritus material to permit the pipeline to descend within a narrow walled trench within the bed of the body of water.

United States Patent [1 1 Perot, Jr.

[ APPARATUS FOR ENTRENCHING SUBMERGED ELONGATE STRUCTURES [75] Inventor:Joseph Charles Perot, Jr.,

Natchitoches, La.

[73] Assignee: Brown & Root, Inc., Houston, Tex. [22] Filed: Feb. 22,1972 [21] Appl. No.: 227,844

Primary Examiner-Jacob Shapiro Attorney-James E. Cockfield [57] ABSTRACTAn apparatus for entrenching submerged elongated [451 Aug. 14, 1973structures such as pipelines and the like, including a skid frame havingport and starboard pontoon runners with a box frame operable to bridgethe pontoon runners over a pipeline to be entrenched. The box frameincludes a first and second set of upper and lower pontoon spanningsupports. Each of the supports includes inwardly facing port andstarboard guide rails. Vertically and horizontally adjustable port andstarboard cutter and eductor heads are ruggedly supported from the boxframe guide rails and extend in close proximity to the surfaces of apipeline to be entrenched. The port and starboard cutter and eductorheads both have a generally vertical-slant-vertical configuration sothat the cutter and eductor heads extend along the lateral surfaces ofthe pipeline, slope beneath the pipeline and extend vertically beneaththe pipeline. The head configuration enables the apparatus to rapidlyand efficiently cut a trench having generally vertical side walls withinthe bed of the body of water and educt the loosened soil or detritusmaterial to permit the pipeline to descend within a narrow walled trenchwithin the bed of the body of water.

19 Claims, 15 Drawing Figures Patented Aug. 14, 1973 7 Sheets-Sheet l NE I a Patented Aug. 14, 1973 3,751,927

.7 Sheets-Sheet 2 dir- FIG. 2

Patented Aug. 14, 1973 3,751,927

7 Sheets-Sheet 5 Patented Aug. 14, 1973 7 Sheets-Sheet 4 Patented Aug.14, 1-973 7 Sheets-Sheet 6 Patented Aug. 14, 1973 .7 Sheets-Sheet '7FIG. I I

APPARATUS FOR ENTRENCIIING SUBMERGED ELONGATE STRUCTURES RELATED PATENTSThis application relates to and is an improvement of U.S. Pat. No.2,755,632 Hauber et al. entitled Submarine Burying Apparatus? I and U.S.Pat. No. 3,338,059 Tittle entitled Methods and Apparatus for EntrenchingSubmerged Elongate Structures" both assigned to the assignee of thesubject application.

BACKGROUND OF THE INVENTION Thisinvention relates to an apparatus forentrenching submerged elongate structures and more particularly to anapparatus for entrenching or burying submarine pipelines.

With the discovery of offshore oil deposits and the subsequent drillingand production thereof, a problem has arisen in connection with aneconomical means of transporting the crude petroleum and gas from adrilling site to a shore collection location or an offshore transferstation. Frequently the most economical means for accomplishing transferhas been to construct submerged pipelines between the producing andcollection locations. In this connection U.S. Pat. Nos. 3,280,571 Hauberet al., 3,390,532 Lawrence, 3,472,034 Lawrence, 3,487,648 Lawrence, and3,507,126 Rochelle et al., assigned to the assignee of the subjectinvention, disclose highly effective processes and apparatus for layingpipeline upon the bed of a body of water.

Shortly following the discovery that pipelines could be economicallylaid on the bed of a body of water significant problems were encounteredin connection with shifting of the line due to currents, pipelinecorrosion, arid pipeline damage caused by anchors, fish nets and similarequipment. In order to obviate or minimize the above noted difficulties,it has been the practice in the past to bury or entrench the submergedpipeline structure beneath the water bed.

In this connection a number of techniques have been successfullyutilized with varying degrees of success. One of the earliest methodsfor burying submerged elongated structures may be discovered byreference to U.S. Pat. Nos. Re. 20,665 Lawton, 2,142,135 Lawton, and2,248,243 Lawton, which disclose in essence a plow structure designed tobe dragged through the water bed by a support vessel. A cable is thenburied within the plow furrow.

While the above technique has achieved a degree of success, it will berealized that deep or large trenches such as are necessary to bury largegas and oil carrying pipelines would be in all essential respectsimpossible to form merely with the above noted plow sleds.

Another known technique for burying submerged pipelines involves theutilization of rotary cutters which are designed to be positionedgenerally beneath a pipeliiie to be entrenched and are driven by fluidor electric motors. The rotary cutters carve out a trench within thewafer lied and thus permit the pipe to descend within the trench.Examples of rotary cutter entrenching machinery may be noted byreference to U.S. Pat. Nos. 3,004,392 Symmank, 3,103,790 Popich,3,238,734- Rhodes, 3,429,131 Martin, 3,429,132 Martih, and 3,583,170 DeYries.

Rotary cutter devices have also been successfully utilized in the pestand'coritiiiiie to be effectively utilized,

however, it will be appreciated that such devices are somewhat elaboratein design requiring as a 'minimum at least one moving cutter head andmotor capable of operation in a submerged environment. Such a device,which must work in a highly corrosive environment, involves many movingparts and is therefore likely to require considerable maintenance andrepair. Moreover, rotary cutters require a significant amount of powerwhich is often difficult to transfer to a deep submerged location.

Alternate devices for entrenching submerged pipelines which are freefrom many of the disadvantages of rotary cutters may be had by referenceto U.S. Pat. Nos. 2,879,649 Elliott, 3,217,499 Isao Ishiki, 3,368,358Elliott, 3,434,297 Grett'er et al., 3,504,504 Elliott, 3,505,826Harmstorf and 3,576,l l1 Henry, Jr. and the above noted U.S. Pat. Nos.2,755,632 Hauber et al. and 3,338,059 Tittle.

The above burying devices are designed for cutting action by focusinghigh pressure fluid streams, from a jetting head, into the water bed.The jetting head typically is supported in an operable posture uponopposite sides of a pipeline to be entrenched by a skid frame. The highpressure fluid jets serve to flush away the soil or water bed and leavea trench in the wake of the burying apparatus.

While such previously known jetting devices are highly advantageous,room for significant improvement remains. In this connection previouslyknown devices have tended to form unnecessarily wide valleys or slopingsided trenches within the water bed. Therefore, unnecessary time andeffort must be expended to backfill the trench. Moreover the rate ofadvancement of the apparatus through the water bed is diminished if anexcessive amount of the water bed is flushed away.

It would therefore be highly desirable to provide an apparatus forentrenching submerged elongated structures which would be capable ofcutting deep and wide submerged trenches to accommodate large pipelinediameters. Further it would be desirable to provide an entrenchingapparatus which would exhibit the characteristics of being relativelyinexpensive initially and highly rugged and reliable in operation whilesimultaneously being efficient and rapid in entrenching a pipelinewithout forming an unnecessarily large trench. Moreover it would beadditionally desirable to provide a rugged entrenching apparatus capableof horizontal and vertical adjustment to accommodate a large variety ofpipeline sizes.

OBJECTS AND SUMMARY OF THE INVENTION OBJECTS It is a general object ofthe invention to provide an apparatus for entrenching submerged elongatestructures which will obviate or minimize problems of the typepreviously described.

It is a particular object of the invention to provide an apparatus forembedding submerged elongate structures which will be simple in designand easily constructed with a minimum number of movable parts.

It is another object of the invention to provide an apparatus forentrenching submerged elongate structures which will be capable ofvertical and horizontal adjustment for utilization with a variety ofpipelinediameters.

It is a further object of the invention to provide an apparatus forentrenching submerged elongate structures which will provide anefficient trench forming operation and minimize the width of the trenchformed to accommodate a particular pipeline being buried.

It is a still further object of the invention to provide an apparatusfor entrenching submerged elongate structures which will be extremelyrugged in design and therefore will be capable of use with largepipelines where deep trenches are required.

It is a specific object of the invention to provide an apparatus forentrenching submerged elongate structures which will have a cutting headassembly operable to minimize the width of a trench formed during aburying operation.

It is a further specific object of the invention to provide an apparatusfor entrenching submerged elongate structures having in combination acutting and eductor head assembly which will minimize the width of atrench formed during a burying operation.

It is another specific object of the invention to provide a jettingapparatus for entrenching submerged elongate structures which will havea ruggedized mounting between a burying sled and at least a cutter headwhich permits horizontal and vertical adjustment of the cutter head withrespect to the sled.

BRIEF SUMMARY An apparatus suitable to accomplish at least some of theforegoing objects comprises a burying sled including port and starboardpontoon runners which support a box frame bridging structure havingfirst and second sets of vertically spaced horizontal spanning beams. Aport cutter and eductor head and a starboard cutter and eductor head arevertically and horizontally adjustably supported upon the first andsecond sets of spanning beams. The port and starboard cutter and eductorheads are operably designed to extend in close proximity along thelateral and lower surfaces of a conduit to be entrenched and verticallybeneath the conduit to be entrenched to form a narrow trench within thebed of a body of water sufficiently wide enough to accommodate theparticular dimensions of the pipeline to be buried while minimizing theamount of the water bed that is cut away, fluidized and removed.

THE DRAWINGS Other objects and advantages of the present invention willbecome apparent from the following detailed description of a preferredembodiment of the invention taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a perspective view of an apparatus for entrenching a submergedpipeline including a control barge operably connected to a submergedburying sled according to a preferred embodiment of the invention;

FIG. 2 is a perspective view of a burying sled including pontoonrunners, a box frame, and vertically and horizontally adjustable portand starboard cutter and eductor heads;

FIG. 3 is a side view of FIG. 2 disclosing the cooperation of theburying sled with a pipeline to be entrenched;

FIG. 4 is a top view of FIG. 2 particularly disclosing apparatus forhorizontally adjusting the port and starboard cutter and eductor headswith respect to a pipeline to be entrenched;

FIG. 5 is a detailed partly broken away end view of the burying sleddisclosing the encompassing relationship exhibited by the port andstarboard cutter and eductor heads with respect to a pipeline to beentrenched.

FIG. 6 is a cross-sectional view taken along section line 66 in FIG. 5and discloses in detail the horizontal adjustment capability of thecutter and eductor heads with respect to the box frame of the buryingsled;

FIG. 7 is a partial view disclosing the port and starboard cutter andeductor head assemblies including a complement of high pressure conduitsconnected thereto;

FIG. 8 is a cross-sectional view taken along section line 8-8 of FIG. 7and further discloses the connection of the cutter head feed conduit,high pressure fluid conduit and eductor conduit;

FIG. 9 is a cross-sectional view taken along section line 99 of FIG. 6and discloses in cross-section the configuration of the eductor conduitwith high pressure fluid lines connected thereto;

FIG. 10 is a cross-sectional view taken along section line 10-10 of FIG.6 and discloses nozzles in the cutter head along with plenum chambersconnected to the eductor head to facilitate injection of high pressurefluid into the interior of the eductor head;

FIG. 11 discloses a detail cross-sectional view taken along section linellll in FIG. 10 and discloses an upwardly directed nozzle through theeductor side wall for directing fluid from a plenum chamber into theinterior of the eductor head;

FIG. 12 is a perspective view of a lock bolt utilized to retain thecutter and eductor heads in a fixed horizontal position with respect tothe burying sled once the cutter and eductor heads are properlypositioned relative to a pipeline to be entrenched;

FIGS. 13-15 (note sheet 1) schematically disclose an operationalsequence for adjusting and positioning the port and starboard cutter andeductor heads around a pipeline to be entrenched including verticallyinserting the cutter and eductor heads over a pipeline, horizontallymoving the cutter and eductor heads to a close encompassing proximitywith the pipeline, subsequently spreading the cutter and eductor headsfollowing the burying operation and lifting the cutter and eductor headsaway from surrounding engagement with the buried pipeline.

DETAILED DESCRIPTION GENERAL STRUCTURE Referring now to the drawings andmore particularly to FIG. 1 thereof there will be seen an elongatestructure 20, such as for example a pipeline, underwater cable or thelike, laying upon the bed 22 of a body of water 24. The pipeline 20 hasbeen previously laid along a desired route by devices such as disclosedin the previously mentioned U.S. Pat. Nos. 3,280,571 I-Iauber, 3,390,532Lawrence, 3,472,034 Lawrence, 3,487,648 Lawrence, and 3,507,126Rochelle.

Subsequent to the laying operation it is often desired to entrench thepipeline within the bed of the body of water. Apparatus to accomplish anentrenching operation by a preferred embodiment of the invention isgenerally disclosed in FIG. 1 and includes a floating marine vessel,such as a burying barge 30, a wishbone 32 connected to the stern of thebury barge, a set of cutter and eductor head lines 34 which lead fromthe wishbone 32 to a port cutter and eductor head combination 36 and astarboard cutter and eductor head combination 38. The cutter and eductorheads are operably designed to I be positioned upon opposite sides of apipeline to be entrenched. The cutter and eductor heads are operativelycarried by a submergeable marine vessel such as a burying sled 40including port and starboard pontoon skids 42 and 44 interconnected by abridging box frame 46. The forward ends of the pontoon skids 42 and 44are connected to the bow of the burying barge 30 by means of a first andsecond wire rope or cable 48.

The bury barge 30 is provided with the usual complement of essentialworking equipment such as, for example, adeck crane 50, a bow boom 52,personnel, storage and equipment quarters 54 and a control bridge 56. AnA-frame 60 is mounted upon the stern of the burying barge and ispivotally supported at its base upon first and second bearing pads 62and 64, respectively. The A-frame may be pivoted about the bearing padsby actuation of a winch 65 which is operatively connected to a block andtackle 67 fitted between the apex of the A-frame and the apex of atripod '66.

The A-frame 60 serves a dual role by first carrying a lower sheath 70 atits apex which serves to guide a pair of wire ropes 72 which extendbetween deck winches 74 on the deck of the barge and mountings on thebox frame 46 of the burying sled 40. By selective actuation of one ormore of the deck winches 74, the burying sled 40 may be verticallyraised or lowered as desired..Secondly the A-frame 60 is provided withan upper sheave 76 which serves to guide a second pair of wire ropes 78which extend between the base leg 86 of the wishbone 32 and the deckwinches 74. Selective actuation of an appropriate deck winch will thusserve to raise or lower the wishbone as desired.

The wishbone 32 includes first and second tines 82 and 84 which arepivotally connected to the stern of the lay barge 30 by first and secondbifurcated mounting brackets 86 and 88. The base leg 80 of the wishbone32 is connected by branch legs to the port and starboard eductor andcutter head lines 90 and 92 which in turn are connected to the port andstarboard cutter and eductor heads 36 and 38. The wishbone 32 serves toconnect lines 90 and 92 with one or more compressors or pumps asdesired. In this connection the interior of the bury barge hull isprovided with fluid jet pumps, suction pumps or compressors and the like(not shown).

Connected to extend over one side of the barge 30 is an exhaust conduit100 which is pivotally supported by an A-frame winch combination 102 andwhich is in fluid communication with one or more of the suction pumpswithin the barge hull.

GENERAL OPERATION In general operation when it is desired to entrench orbury a previously laid elongate conduit 20 within the bed of a body ofwater, the bury barge 30 is positioned generally vertically above thepipeline. The burying sled, 40 is then lowered from the A-frame 60 untilthe port and starboard cutter and eductor heads 36 and 38 straddle apipeline to be entrenched. As previously mentioned the burying'sled 40is connected to the bow of the bury barge 30 by wire ropes 48 suspendedfrom a boom 52. Thus, as the barge 30 is navigated along the conduitroute by the utilization of well known anchor winching techniques theburying sled 30 will be pulled along the conduit.

In order to entrench the conduit within the bed of the body of waterpumps within the hull of the bury barge 30 pump high pressure fluid downthe high pressure lines and into the port and starboard cutting heads.The high pressure fluid is released through orifices in the cutting headand jets against the water bed to fragment and erode away the soil.Eductor heads are positioned adjacent to each of the cutting heads andby means of a suction pump within the barge hull the fluidized detritusmaterial may be withdrawn from the volume surrounding the pipeline andpumped over the side of the bury barge 34} through conduit 100. As theseabed is cut away by the jetting head, fragmentized and subsequentlyremoved by the eductor system, it will be appreciated that thenegatively buoyant elongate conduit 20 will descend within the trenchand thus be buried within the water bed. The depth of the trench willvary according to the particular circumstances but depths from a fewfeet to 15 or more feet may be provided with the subject apparatus.

An alternative means of educting the fluidized detritus material fromadjacent the pipeline comprises running high pressure air conduits downto the eductor heads and tapping the high pressure conduits into thelower portions thereof to provide air bubbles with the eductor linewhich will serve to lift the particulate material by a gas lifttechnique.

In some instances it is preferred to lift the detritus material up tothe vessel and dump it overboard through exit conduit 1100 as previouslydiscussed. However, in other instances when using the gas lift techniqueit may be preferred merely to direct the detritus material away from theimmediate area of the trench. In such event the eductor lines need notextend up to the bury barge but may be merely directed away from thefreshly cut trench.

It will be appreciated that individual barges may vary slightly from theabove in terms of equipment and operation, however, as a generalillustrative matter the above description is accurately representative.

THE BURYING SLED Referring now particularly to FIGS. 2, 3 and 4, therewill be seen in perspective, side and top detailed views, respectively,a preferred embodiment of the burying sled 40. As previously mentioned,the burying sled includes a port pontoon skid 42 and a starboard pontoonskid 441. The pontoon skids are generally hollow and are provided withhemispherical end caps MM) and W2, respectively, at the stern endsthereof and sloping face plates MM and 1106 at the bow ends thereof todefine fluid tight variable buoyancy chambers. Ballast valves H08 andblowing valves 11 M) are connected into each of the port and starboardpontoon skids. These valves may be conventional hand-operated structuresor remotely controllable as desired. In this connection high pressureconduits may be connected to the valves, selectively or permanently.

As specifically illustrated in FIGS. 3 and 5, each of the pontoon skids42 and 441 may be fitted with abrasion wrappers 1112 and M41,respectively. The abrasion wrappers or plates have an arc shapedcross-section which enables them to be fitted in juxtaposition with thebottom curved portions of the pontoon skids and thus to functionallyenhance the rigidity and wear characteristics of the pontoon runners.

First and second towing pad eyes 120 and 122 are fixedly connected tothe bow end of the port and starboard pontoon skids 42 and 44 to providea ready junction source for wire cables 48 extending from the vessel 30to the burying sled 40.

The port and starboard pontoon skids 42 and 44 have generally parallellongitudinal axes and as previously mentioned are operably designed toslide along the bed of a body of water upon opposite sides of a pipelineto be entrenched within the water bed. The pontoon skids 42 and 44support a bridging box frame structure 46 which includes upstandinggenerally vertical posts or columns 130, 132 and 134 connected to theupper surface of the port pontoon 42 and upstanding posts or columns136, 138 and 140 connected to the starboard pontoon 44.

Columns 130 and 132 are interconnected for structural rigidity by ahorizontal brace 142 and a sloping strut 144. In like manner, columns136 and 138 are structurally interconnected by a brace 146 and a strut148.

Column 132 is interconnected with column 134 by upper and lower sidebraces 150 and 152, respectively. Columns 138 and 140 in like manner areinterconnected by upper and lower side braces 154 and 156, respectively.The upright columns 130, 132 and 134 and upright columns 136, 138 and140 are thus structurally interconnected by a rigid latticework ofbraces and struts. The rearmost or stem columns 134 and 140 may beadditionally supported by batter braces 158 and 160, respectively. Thebraces and struts are depicted as being formed from tubular members,however, it will be realized that other structural designs such as I-beams, T-beams, L-channels and the like, may be effectively utilized ifdesired.

Normally extending lifting pad eyes 174, 176, 178 and 180 are fixedlyconnected to the uppermost portion of columns 130, 134, 136 and 140,respectively, to provide an attachment junction for wire ropes 182, 184,186 and 188, respectively, which in turn are united at a location abovethe burying sled 40 and connected to steel cables 72 for facilitatingraising and lowering movement of the burying sled, as previouslydescribed.

Columns 132 and 138 are interconnected by upper and lower verticallyspaced horizontally extending spanning beams 162 and 164, respectively.Note FIG. 6. In like manner, columns 134 and 140 are interconnected bygenerally horizontally extending vertically spaced upper and lowerspanning beams 166 and 168, respectively. The lower horizontal beam 168may additionally be interconnected with the starboard and port pontoonsby first and second generally horizontally sloping braces 170 and 172,respectively.

As described above and as best illustrated in FIGS. 2-6 the uprightcolumns 132, 134, 138 and 140 together with the upper and lower sidebraces and upper and lower spanning beams form a generally rectangularbox frame 46 which normally spans and interconnects the port andstarboard pontoon skids 42 and 44 and thus in all material respects willoperationally serve as a bridge frame over a pipeline to be entrenched.

CUTTER AND EDUCTOR HEAD ADJUSTABLE CONNECTIONS Adjustably positionedinteriorly within the above described generally rectangular box frame 46are port and starboard cutter and eductor heads 36 and 38, respectively.

As best illustrated in FIGS. 2 and 6 the port cutter and eductor head 36is provided with a plurality of cantilever fore supporting arms 200, 202and 204 which are vertically spaced and fixedly connected at one end tothe outer periphery of the fore portion of eductor head 206. Thecantilever support arms 200, 202 and 204 are also fixedly connected tocutter head 208 which extends in a generally coextensive posture witheductor head 206 in a manner which will be described in detailhereinafter.

A second plurality of cantilever generally horizontally extendingvertically spaced support arms 210, 212 and 214 are fixedly connected atone end to the outer periphery of an aft portion of the eductor head206.

The starboard cutter and jetting head, in a similar manner, and asillustrated in FIG. 2, is provided with a plurality of generallyhorizontally extending and vertically spaced cantilever support arms216, 218 and 220 which are fixedly connected to a fore portion of thestarboard eductor head 222 and which are also fixedly connected to astarboard cutter head 224. Moreover a plurality of generallyhorizontally extending and vertically spaced cantilever support arms226, 228, 230 extend from an aft portion of the eductor head 222.

While only three generally fore and aft support arms have been disclosedin connection with the port and starboard cutter and eductor heads itwill be appreciated by those skilled in the art that the abovementionedplurality of cantilever support arms may include a substantially greaternumber as increased vertical adjustment capability is desired.

Referring now to FIG. 6 cantilever support arms 200, 202 and 204 arefitted at the free ends thereof with identical bearing and lockingplates 232, 234 and 236, respectively. Illustrative of the plates 232,234 and 236 is plate 232 which is shown provided with a generally planerrectangular bearing face 235, as best illustrated in FIGS. 5 and 6. Thebearing plate 232 is provided in a lower portion thereof with first andsecond horizontally spaced locking apertures 238 and 240, the functionof which will be discussed in detail hereinafter. The aft cantileversupport arms 210, 212 and 214 of the port eductor head are in a likemanner fitted with bearing and locking plates 246, 248 and 250,respectively. Plates 246, 248 and 250 are provided with lockingapertures in a lower portion thereof identical with previously discussedlocking plates 232, 234 and 236.

The fore starboard cutter and eductor head cantilever support arms 216,218 and 220 are in a like manner provided with bearing and lockingplates 252, 254 and 256, respectively. Similarly the aft starboardsupport arms 226, 228 and 230 are provided with identical bearing andlocking plates 258, 260 and 262.

As previously described the locking plates are all provided in a lowerportion thereof with first and second locking apertures. Moreover eachof the above described locking and bearing plates are provided with aT-shaped support runner 270, note pad 232 in FIG. 6.

Each support runner 270 includes a body web 272 which extends generallyhorizontally and transverse to the major axes of the eductor and cutterheads. The body web 272 functionally forms an upper 274 and a lower 276horizontally extending bearing surface. The body web 272 is fitted at afree end thereof with a normally postured head plate 278 which providesa planer outwardly facing vertical bearing surface 280 and an innerupper vertical bearing surface 282 and an inner lower vertical bearingsurface 284. Moreover the top 285 and bottom 287 edge portions of headplate 278 provide generally horizontally extending top and bottombearing surfaces.

While the T-shaped support runners 270 have only been specificallydescribed in connection with bearing and locking plate 232 it will beappreciated that each of the bearing and locking plates are providedwith an identical T-shaped support runner.

Referring now to FIGS. 2 and 5 the upper and lower horizontallyextending fore beams 162 and 164 are each provided with port,upper andlower and starboard,upper and lower guide rails 300, 302 and 304, 306,respectively. In like manner the upper and lower horizontally extendingaft beams 166 and 168 are provided with port,upper and lower andstarboard, upper and lower guide rails 310, 312 and 314, 316. Each ofthe guide rails are identically constructed and therefore the followingdetailed description in connection with guide rail segment 302, asparticularly illustrated in FIGS..5 and 6, is equally applicable to theremaining guide rail segments.

Guide rail segment 302 includes an upper horizontally extending plate310 and a lower horizontally extending plate 312 both of which arefixedly connected at one of the ends thereof to an upper and lowersurface respectively of horizontal beam 164. A downwardly, verticallyextending plate 314 is connected to an inner surface 316 of upper plate310 at the free end thereof and an upwardly vertically extending plate318 is connected to an inner surface 320 of plate 312 at the free endthereof. The upper plate 314 and lower plate 318are longitudinallyextending and have inner bearing surfaces 322 and 324 respectively. Thefree edges of the upper plate 314 and lower plate 318 extend toward eachother to form horizontally extending inner rail surfaces 326 and 328,respectively. A web 330 is connected between the inner surface 316 ofplate 310 and the inner surface 320 of plate 312 at about a midspanportion thereof and abuts against a rear portion of of horizontal brace164. Web 330 operably provides a horizontally and vertically extendinginner bearing surface 332.

It will now be seen that the above described members and plates combineto define a generally T-shaped sliding guide bound, and thus defined, byinner bearing surfaces 332, 310, 322, 326, 328, 324 and 320. Each of theguide members are dimensioned such that the T-slot formed by the innerbearing surfaces are compa'tible with and slightly greater than theexterior surfaces of a respective T-slide 270 so that an intimate fitmay be achieved to provide a rugged supporting junction which willeliminate any rocking motion of the cutter and eductor heads whilesimultaneously providing a horizontal adjustment capability.

The horizontal guide rails each include a locking assembly comprising afirst downwardly extending plate 350 normally connected to the bearingplate 312. Locking plate 350 is provided with a plurality of apertures352 as best illustrated in FIG. 5. Vertically displaced below each ofthe locking apertures 352 are re taining studs 354 which normally extendoutwardly from the locking plate 350.

A horizontally extending base 356 extends rearwardly from the lockingplate 350 and serves to support first and second normally extendingspaced retainer plates 358 and 360. Retainer plates 358 and 360 are eachprovided with a plurality of apertures 362 and 364 respectively whichare coaxially aligned with locking apertures 352 fashioned through thelocking plate 350. Retainer plates 358 and 360 are operatively spaced onthe base plate 356 so that when a T-slide 270 is positioned within aguiding rail the lower portion of the bearing and locking plate will besnugly received between the securing plates 358 and 360. The apertures238 and 240 in the bearing and locking plates are spaced from the bottomthereof so as to have axes which will be alignable with the axes oflocking apertures 362, 364 and 352.

Once the apertures 362, 364 and 352 and the apertures 238 and 240 arebrought into alignment a pair of locking bolts or pins 380 may bemanually slid into position to lock the plate to the guide rail and thusfix horizontal movement of the cutter and eductor heads with respect tothe box frame.

In the above connection a detail view of a locking bolt or pin 380 isshown in FIG. 12. The pin 380 is formed having a solid shaft 382dimensioned to be snugly receivable within apertures 362, 364 and 352. Aretaining ring or lip 384 surrounds a mid portion of the shaft 382 andserves to limit axial movement of the pin between plate 360 and plate350 so that the pin may not be lost in a submerged environment during anadjustment operation. The pin 380 is also fitted with a generally pearshaped end cap 386 having a slot 388 formed in a lower neck portionthereof. The slot 388 is dimensioned to be slidable over a correspondingnormally projecting stud 354. A nut 390 is connected to the end cap 386by a suitable flexible connector 392 and is designed to be manuallyengageable with stud 354 so that the pin 380 may be normally retained ina locking posture.

In a preferred embodiment each of the apertures 352 are provided with alocking pin 380. In an alternate embodiment, however, individualapertures 352 may be replaced by a horizontally extending slot (notshown} and therefore only two locking pins 380 would be utilized, one toaccommodate each of the pair of apertures in the lower portion of thelocking plates.

, The horizontal extent of each of the guide and locking rails is from aposition adjacent to a corresponding upright column of the box frame toa location spaced from the center of the bearing sled, as bestillustrated in FIGS. 2 and 5.

In order to effectuate horizontal adjustment of the port and starboardcutter and jetting heads 36 and 38 first and second horizontallyactuatable fluid motors 370 and 372 are provided, as illustrated inFIGS. 2 and 4. Fluid motor 372 is pivotally connected at the endsthereof between a base plate 374 which extends between horizontal boxframe side braces 154 and 156 and a pivotal bearing pad 376 mounted upona lateral surface of the starboard eductor head 222. The fluid motor 372comprises a piston and cylinder assembly 378 which may be wateractuatable in a manner well known in the art. In this connection fluidlines (not shown) connect the cylinder with a source of pressurizedfluid which typically is maintained on board barge 30.

An identical fluid motor 370 is connected on the port side of theburying sled and functions in cooperation with fluid motor 372 tohorizontally slide the cutter and eductor heads 36 and 38 on the guiderails to position the cutter and eductor heads optimumly with respect toa pipeline to be buried. After the pipeline is snugly surrounded by thecutter and eductor heads the locking pins 380 may be manually lockedinto place to retain the proper horizontal spacing of the cutter andeductor heads throughout the burying operation.

CONDUIT GUIDES AND REMOTE SENSING APPARATUS Referring now to FIGS. 3-6and 9 there will be seen a plurality of fore and aft supporting rollers600 and 602 designed to encompass a pipeline to be buried and thusmaintain the sled in a porperly aligned posture with respect to thecentral axis of a pipeline to be entrenched.

Referring now specifically to FIG. 5, it will be seen that the pluralityof fore guide rollers 600 include an upper roller 604 having a generallyhorizontally extending axis, a pair of side rollers 608 and 610 havinggenerally vertically extending axes, and a pair of bottom rollers 612and 614 having inwardly sloping axes.

The upper roller 604 and the side rollers 608 and 610 are all pivotallymounted within bifurcation brackets fixedly connected to the horizontalbeam 164 and the eductor heads 206 and 222 respectively and are designedto actuate load cells associated therewith to signal at a remotelocation contact of the pipeline with the rollers. In an individualstructural and functional manner the rollers, mountings, load cells andremote indicators associated therewith are identical with thosedisclosed in US. Pat. No. 3,507,]26 Rochelle et al., particularly inconnection with FIGS. 7 and 8 of the drawings and columns l2-l4 of thespecification. The above noted pertinent portion of the Rochelle et al.patent is hereby incorporated by reference as though set forth atlength.

Positioned generally beneath the elongated conduit are port andstarboard inclined supporting roller assemblies 612 and 614,respectively. These roller assemblies unlike the previously describedtop and side roller assemblies 604, 608 and 610 are not pivotallymounted and connected to load cells but rather are merely rotatablyattached between bifurcation bracket such as bracket 620 supportingroller 612 as illustrated in FIG. 6.

The stern set of rollers 602 are identical in structure and individualfunction with the forward set of rollers 600 and serve in cooperationtherewith to maintain the sled in a properly aligned posture withrespect to the elongate structure to be entrenched.

In this regard and as previously alluded to each of the verticallyextending laterally engaging side rollers have load sensing cellsassociated therewith and may be connected to indicators on board vessel30. The fore and aft horizontally extending top rollers also areprovided with load sensing cells which feed signals to indicators onboard the barge 30. Thus, an operator on board can monitor vertical andhorizontal displacement of the sled with respect to the pipe and alsovertical and horizontal rotational canting of the sled with respect tothe pipeline. In this connection vertical canting of the sled about ahorizontal axis is a highly significant parameter to monitor in that animbalance of fore and aft readings may indicate that the sled cutterheads have encountered an immovable object or that the sled advance rateis too great for the particular soil encountered. Thus it is possible byskillful manipulation of the barge anchor winches to maintain anapproximately parallel relationship of the longitudinal axes of the sledrunners with respect to the longitudinal axis of the elongate structureto be entrenched during the entrenching operation and further tomaintain an appropriate sled advance rate.

CUTTER AND EDUCTOR HEADS Referring now particularly to FIGS. 7 and 8there will be seen in combination cutter and eductor head assemblies 36and 38 forming a further specific aspect of the subject invention.

The cutter and eductor heads are connected to service line bundles and92. Service lines 92 include an eductor conduit 400, a high pressure airconduit 402 and a high pressure fluid conduit 404. The service lines 90include an eductor conduit 406, a high pressure air conduit 408 and ahigh pressure fluid conduit 410.

Conduits 404 and 402 of the cluster of service conduits 92 areinterconnected by horizontal brace members 412 which are spacedvertically from one another to maintain a spatial relationship betweenthe service conduits. In a like manner conduits 400 and 402 are providedwith horizontal braces 414 and conduits 400 and 402 are interconnectedby horizontal brace members 416. Thus at spaced elevations the conduits400, 402 and 404 are fixedly interconnected by triangular bracearrangements of bracing members 412, 414 and 416.

In a similar manner the cluster of service conduits 406, 408 and 410which comprise service lines 90 are interconnected by a triangularbracing network including horizontal braces 418 interconnecting theconduits 408 and 410.

The lower ends of conduits 400 and 404 are connected through flangefittings 430 and 432 to an eductor head 222 and a cutter head 224. Thehigh pressure air conduit 402 is connected through a flange fitting 434to lead conduit 436 which in turn connects into a high pressure plenumchamber 438 surrounding the eductor head 222 as best illustrated inFIGS. 2 and The eductor head 222, the cutter head 224 and the highpressure air conduit extension 436 are interconnected by a generallyhorizontally extending triangular brace arrangement including horizontalmembers 440, 442 and 444 immediately below the flange connections 430,432 and 434.

In like manner the port service lines 90 are connected through flangefittings 442 and 444 to the port eductor head 206 and the port cutterhead 208. The high pressure conduit 408 is connected through a flangefitting 446 to an extension 448 which leads into a high pressure plenumchamber 450 which like plenum chamber 438 surrounds a correspondingeductor head.

The eductor head 206 and cutter head 208 are interconnected with eachother and the high pressure air conduit extension 448 by a horizontaltriangular brace arrangement which includes horizontal brace 452.

The particular shape of the cutter and eductor heads downstream of theplenum chamber is a highly significant aspect of the subject inventionand will now be described in detail. More particularly and referring toFIG. 7 of the drawings it will be seen that the starboard cutter headassembly 224 includes an upper first segment 460 having a centrallongitudinal axis A-A which is generally vertically extending and isoperable to be positioned along a lateral surface of a submerged conduitto be entrenched. The lower end of the first cutter head conduit segment460 is connected to a second cutter head conduit segment 462 which isprovided with a central longitudinal axis B-B which extends at an obtuseangle X with respect to the central longitudinal axis AA of the firstconduit segment 460. The

lower portion of the second cutter head conduit segment 462 is connectedto a'third cutter head conduit segment 464 which has a centrallongitudinal axis C-C which extends at an obtuse angle Y with respect tothe central longitudinal axis of the second cutter head conduit segment462.

Positioned adjacent to and extending generally coextensive with theabove described starboard cutting head is a starboard eductor head 222.The starboard eductor head 222 includes a first conduit segment 466which extends generally vertically and has a central longitudinal axisA'A extending parallel with the central longitudinal axis A-A of thefirst cutter head conduit segment. Connected to the lower end of thefirst eductor head conduit segment 466 is a second eductor head conduitsegment 468 having a central longitudinal axis B'B' extending parallelwith the axis of the second cutter head conduit segment B-B and at anobtuse angle X with respect to the central longitudinal axis A'A' of thefirst eductor head conduit segment 466. Connected to the free end of thesecond eductor head conduit segment 468 is a third eductor head conduitsegment 470 which has a central longitudinal axis C'-C' which extendsgenerally parallel with the central longitudinal axis C-C of the thirdcutting head conduit segment 464 and at an obtuse angle Y with respectto the central longitudinal axis BB of the second eductor head conduitsegment 468.

Referring now to the port cutter and eductor head assembly 33, therewill be seen a cutter head 208 which includes a first cutter headconduit segment 472 having a central longitudinal axis D-D extendinggenerally vertically and is operably adapted to be positioned adjacentto a lateral surface of a submerged elongate conduit to be entrenched.Connected to the free end of the first cutter head conduit segment 472is a second cutter head conduit segment 474 having a centrallongitudinal axis E-E lying at an obtuse angle W with respect to thecentral longitudinal axis D-D of the first cutter head conduit segment472. Connected to the free end of the second cutter head conduit segment474 is a third cutter head conduit segment 476 having a centrallongitudinal axis F-F lying at an obtuse angle Z with respect to thecentral longitudinal axis E-E of the second cutter head conduit segment474.

Positioned adjacent to and extending generally coextensively with theport cutter head 208 is eductor head 206 which includes a first conduitsegment 478 having a central longitudinal axis D'D extending generallyparallel with respect to the central longitudinal axis D-D of the firstcutter head conduit segment. Connected to the lower end of the firsteductor head conduit segment 478 is a second eductor head conduitsegment 480 having a central longitudinal axis E'E lying generallyparallel with the central longitudinal axis E--E of the second cutterhead conduit segment 480 and at an obtuse angle W with respect to thecentral longitudinal axis D'D' of the first eductor head conduit segment478. Connected to the free end of the second eductor head conduitsegment 480 is a third eductor head conduit segment 482 having a centrallongitudinal axis F'F' lying generally parallel with respect to the axisFF of the third cutter head conduit segment and at an obtuse angle Zwith respect to the central longitudinal axis E-E of the second eductorhead conduit segment.

From the above detailed description it will be realized that the cutterand eductor heads 36 and 38 may be generally characterized as extendinggenerally vertically downwardly along the lateral surfaces of asubmerged elongated conduit to be entrenched, inwardly beneath a lowerportion of a conduit to be entrenched and then generally verticallyagain downwardly beneath the submerged conduit to be entrenched. Thisvertical-slant-vertical cutter head arrangement enables a narrow trenchto be formed within the bed of the body of water and thus minimizesproblems of the type previously described.

Referring now to FIGS. 9 and 10 there will be seen cross-sectional viewstaken along section lines 9-9v and 1111-10 of the port cutter andeductor head 36 as seen in FIG. 6.

With particular reference now to P16. 9, the first conduit segment 472of the cutting heads is shown spatially fixed with respect to the firstconduit segment 478 of the eductor head 206 by a generally horizontallyextending brace 5M1.

The first conduit segment of the eductor head is formed having a pair ofspaced generally parallel side walls 502 and 5614 which are connected attheir ends by semicircular end wall sections 506 and 5118. Thecrosssectional configuration,therefore, of the eductor head may begenerally described as being somewhat elliptical or a circularcross-sectional configuration with an expanded central section.

Referring back to FIG. 6, the high pressure connecting air conduit 8feeds into a plenum chamber 4511 as previously described. The plenumchamber has tapped into it four conduits 511B, 512, 514 and 516. Theseconduits extend along the exterior surface of the eductor head 2116 andhave mutually parallel axes which in turn are generally parallel withthe major central longitudinal axis of the eductor head. The conduitsSW, 512, S14 and 516 are shielded and protected from displacement bychannel covers 5241, 522, 524 and 526, respectively, which surround theconduits and are fastened to the exterior of the eductor head.

As best illustrated in FIGS. 6 and 10, the conduits 510, 512, 514 and516 exit from their shielding covers 520-526 and feed into individualaccumulation chambers 531), 532, 534 and 536, respectively.

FIG. 111 discloses a partial cross-sectional view taken along sectionline 11-11 in FIG. 10 and illustrates a feed conduit 516 feeding into acorresponding accumulation chamber 536 which in turn surrounds anupwardly directed nozzle 540. Nozzle 540 is operable to direct fluidinto the eductor conduit in a generally upward direction. in thisconnection, arrows J, K and L in FIG. 11 indicate the path of fluid flowinto the eductor head. With the circumferentially spaced locations ofeach of the accumulation chambers 5341-536 and an upwardly directednozzle through the eductor head wall, associated with each chamber, itwill be seen that a circumferential inward flow of fluid may be achievedas indicated by arrows L, M, N and O in N6. 111. Such symmetric flowwill serve to promote uniform commingling of gas and detritus materialwithin the eductor head to the end that the specific gravity of thedetritus solution within the eductor head will be reduced, thus liftingthe material up through the eductor by the well known gas lifttechnique.

A plurality of jetting apertures 545 are positioned through the walls ofthe first, second and third conduit segments of each cutter head as bestillustrated in FIGS. 2, 3, 5 and 6. As previously mentioned highpressure fluid may be jetted through apertures 545 to erode away thewater bed. In some instances the eroding action may be accentuated byadding nozzles within the apertures. In this connection as seen in FIG.10, a nozzle 552, 554 and 556 may be positioned within each of theapertures 546, 548 and 550 as desired to direct high pressure fluid intoa water bed formation. The particular selection of nozzles and thespecific pattern of application may vary depending upon the type of soilencountered to most efficiently and rapidly cut away the submergedformation. One form of satisfactory nozzle design is disclosed in a U.S.Pat. No. 3,597,930 R0- chelle, note particularly FIGS. 8 and 9 andcolumn 6 of the specification. The pertinent portion of the above notedRochelle patent is hereby incorporated by reference as though set forthat length.

ADJUSTMENT OPERATION AND ADAPTATION FOR VARYING PIPELINE SIZES Inoperation when it is desired to entrench a submerged pipeline, theexterior size of the pipeline is determined and the port and starboardeductor heads are vertically adjusted on board the barge to accommodatethe pipeline in a triangular bearing posture within the top, side andbottom rollers 600 and 602.

Vertical adjustment is achieved by disconnecting fluid motors 370 and372 and withdrawing all the locking pins 380. The eductor heads 36 and38 are then slid along the guide rails toward the center portion of thesled where the T-connections may be disengaged with correspondingguides. Vertical shifting adjustment may then be performed and analternate pair of T-shaped runners are slid into the upper and lowerguide rails. For structural rigidity it will be appreciated that in apreferred embodiment an upper and lower connection is always maintainedbetween the T-shaped runners and the guide rails. The horizontal fluidmotors are then reconnected for subsequent submerged horizontaladjustment.

The burying sled is then lowered over the stern of the barge supportedby the A-frame into a general posture such as that depicted in FIG. 1.The horizontal spacing of the axes of the third conduit segments of theeductor and cutter heads at this point in time are greater than thediameter of the pipeline to be entrenched as particularly disclosed inFIG. 13. High pressure fluid is then jetted through the cutter heads 208and 224 until the seabed 22 is flushed away adjacent the pipeline. Thecutter and eductor heads may then descend within the water bed andsurround the conduit to be entrenched, as illustrated in FIG. 14. Atthis point in time the fluid motors 370 and 372 will be actuated tohorizontally close the cutter and eductor heads about the pipeline to beentrenched. When the pipeline is snugly encompassed a diver manuallyreinserts all of the locking pins 380 into the apertures in the lockingrails to fixedly position the cutter and eductor heads and the buryingoperation progresses as previously described.

In this connection it will be appreciated that the seabed 22 to be cutaway will cross-sectionally correspond to the vertical-slant-verticalconfiguration of the cutter and eductor heads as particularlyillustrated in FIG. 5 and thus a minimum amount of the seabed will beflushed away, thereby enabling the pipeline to descend within the bed ofthe body of water and be readily covered in a rapid and efficientmanner.

Upon completion of the burying operation a diver will again descend tothe burying sled and loosen and withdraw all of the locking pins 380.The cutter and eductor heads may then be horizontally separated byactuation of fluid motors 370 and 372 as illustrated in FIG. 15. Thesled may then be raised by the A-frame and repositioned upon the bargefor transportation to another location as desired.

SUMMARY OF THE MAJOR ADVANTAGES It will be appreciated that the abovedescribed apparatus provides a considerable advantage in the performanceof entrenching submerged elongate structures. Particular advantages areprovided by the simplicity of design of the overall entrenchingapparatus without utilizing submerged moving parts. In this connectionthe water bed is eroded away by the provision of fluid jets and thedetritus material is then removed by a suction or gas lift system.Therefore it will be appreciated that submerged relative moving membersare not required.

Moreover the subject entrenching apparatus is extremely rugged in designand may therefore be effectively utilized with large and weightyconduits without requiring an excessive amount of repair or maintenance.

The particular ruggedized horizontal and vertical adjustment connectionspermit the subject apparatus to accommodate a plurality of conduitdiameters without sacrificing the capability of the apparatus to performdeep burying operations which require extremely rugged equipment.

A specific advantage of the subject invention comprises the particularconfiguration of the port and star board cutter heads which mayfiguratively be described as vertical-slant-vertical. Such a headconfiguration enables the width of the trench to be minimized thuspromoting cutting advancement rate and concurrently diminishing backfilling requirements.

Associated with the advantages provided with the cutter headsconfiguration are those afforded by a similar vertical-slant-verticalconfiguration of the eductor heads which provide an efficient removal ofdetritus material from within the narrowly cut trench.

While the invention has been described with reference to a preferredembodiment, it will be appreciated by those skilled in the art thatadditions, deletions, modifications and substitutions or other changesnot specifically described, may be made which will fall within thepurview of the appended claims.

What is claimed is: 1. An apparatus for entrenching a submerged pipelineand the like within the bed ofa body of water comprising:

a frame operable to be lowered over and transported along a submergedpipeline to be entrenched; and

means connected to said frame for cutting a trench beneath a submergedpipeline within the bed of the body of water comprising,

a first cutter head including a first conduit segment having a centrallongitudinal axis operably positionable generally vertically along oneside of a pipeline to be entrenched, said first conduit segment having,

a plurality of jetting apertures fashioned therein,

second conduit segment connected at one end to said first conduitsegment, said second conduit segment having a central longitudinal axisextending at an obtuse angle with respect to the central longitudinalaxis of said first conduit segment, said second conduit segment having,

a plurality of jetting apertures fashioned therein,

a third conduit segment connected at one end to the other end of saidsecond conduit segment, said third conduit segment having a centrallongitudinal axis extending at an angle with respect to the centrallongitudinal axis of said second conduit segment and generally parallelwith respect to the central longitudinal axis of said first conduitsegment, said third conduit segment having,

a plurality of jetting apertures fashioned therein, and

a second cutter head including,

a third conduit segment connected at one end to the other end of saidsecond conduit segment, said third conduit segment having a centrallongitudinal axis extending at an angle with respect to the centrallongitudinal axis of said second conduit segment and generally parallelwith respect to the central longitudinal axis of said first conduitsegment, said third conduit segment having,

a plurality of jetting apertures fashioned therein,

wherein said first conduit segments of said first and second cutterheads have generally mutually parallel central longitudinal axes and areoperatively adapted to extend generally vertically on opposite sides ofa pipeline to be entrenched, and said third conduit segments of saidfirst and second cutter heads have generally mutually parallel centrallongitudinal axes and extend generally vertically beneath a pipeline tobe entrenched whereby the perpendicular distance between the generallymutually parallel longitudinal axes of said first conduit segments isgreater than the perpendicular distance between the generally mutuallyparallel longitudinal axes of said third conduit segments. 2. Anapparatus for entrenching a submerged pipeline and the like within thebed of a body of water as defined in claim 1 and further comprising:

means connected to said frame for withdrawing particles of fluidizedmatter from adjacent said means for cutting comprising,

a first eductor head having first, second and third conduit segmentspositioned adjacent to and extending generally coextensive with saidfirst, second and third conduit segments respectively of said firstcutter head, and

a second eductor head having first, second and third conduit segmentspositioned adjacent to and extending generally coextensive with saidfirst, second and third conduit segments respectively of said secondcutter head.

3. An apparatus for entrenching a submerged pipeline and the like withinthe bed of a body of water as defined in claim 2 and further comprising:

means connecting said first cutter head and said first eductor head tosaid frame for independent horizontal and vertical adjustability thereofwith respect to said frame, and

means connecting said second cutter head and said second eductor head tosaid frame for independent horizontal and vertical adjustability thereofwith respect to said frame.

4. An apparatus for entrenching a submerged pipeline and the like withinthe bed of a body of water comprising:

a burying sled, including first and second pontoon skids havinggenerally mutually parallel longitudinal axes, said pontoon skids beingoperably spaced to straddle a submerged pipeline to be entrenched, and

a box frame bridging said first and second spaced pontoon skidsincluding,

a first set of upper and lower vertically spaced horizontally extendingspanning beams connected between said first and second spaced pontoonskids and extending generally norsaid pontoon skids, and a second set ofupper and lower vertically spaced horizontally extending spanning beamsconnected between said first and second spaced pontoon skids andextending generally normally with respect to the longitudinal axes ofsaid pontoon skids, said second set of spanning beams extendinggenerally parallel with respect to said first set of spanning beams andbeing offset with respect thereto,

a cutter and eductor head operably mounted between said first set ofspanning beams and said second set of spanning beams on the port side ofsaid burying sled for independent vertical and horizontal adjustmentwith respect thereto; and

a cutter and eductor head operably mounted between said first set ofspanning beams and said second set of spanning beams on the starboardside of said burying sled for independent vertical and horizontaladjustment with respect thereto.

5. An apparatus for entrenching a submerged pipeline and the like withinthe bed of a body of water as mally with respect to the longitudinalaxes of j defined in claim 4 wherein said first and second pontoon skidsinclude:

first and second longitudinally extending plate members having an arcshaped cross-sectional configuration connected in juxtaposition to abottom portion of said first and second pontoon skids respectively.

6. An apparatus for entrenching a submerged pipeline and the like withinthe bed of a body of water as defined in claim 4 and further comprising:

upper and lower guide rails connected on the port side of said first setof spanning beams to said upper and lower vertically spaced spanningbeams respectively;

upper and lower guide rails connected on the starboard side of saidfirst set of spanning beams to said upper and lower vertically spacedspanning beams respectively;

upper and lower guide rails connected on the port side of said secondset of spanning beams to said upper and lower vertically spaced spanningbeams respectively; and

upper and lower guide rails connected on the star board side of saidsecond set of spanning beams to said upper and lower vertically spacedspanning beams respectively.

7. An apparatus for entrenching a submerged pipeline and the like withinthe bed of a body of water as defined in claim 6 wherein said guiderails include:

generally horizontally extending T-shaped slots.

8. An apparatus for entrenching a submerged pipeline and the like withinthe bed of a body of water as defined in claim 6 and further comprising:

a plurality of lock rails, one being connected to and extendinggenerally coextensive with each of said upper and lower, port andstarboard guide rails on said first set of spanning beams and saidsecond set of spanning beams.

9. An apparatus for entrenching a submerged pipeline and the like withinthe bed of a body of water as defined in claim 8 wherein each of saidlock rails includes:

a plurality of horizontally spaced locking apertures;

and

a locking bolt operably connected to the locking rail adjacent each ofsaid horizontally spaced locking apertures.

10. An apparatus for entrenching a submerged pipeline and the likewithin the bed of a body of water as defined in claim 6 and furthercomprising:

a plurality of vertically spaced horizontally extending cantileversupport arms extending from each of the fore and aft portions of saidport and starboard cutter and eductor heads, each one of said supportarms is fitted with an end element and connected thereto,and

said support arms being operably vertically spaced so that,

a pair of the plurality of support arms extending from the fore portionof said port cutter and eductor head are selectively engageable with theupper and lower guide rails on the port side of said first set ofspanning beams, and

a pair of the plurality of support arms extending from the aft portionof said port cutter and eductor head are concurrently selectivelyengageable with the upper and lower guide rails on the port side of saidsecond set of spanning beams, and a pair of the plurality of supportarms extending from the fore portion of said starboard cutter andeductor head are selectively engageable with the upper and lower guiderails on the starboard side of said first set of spanning beams, and apair of the plurality of support arms extending 10 from the aft portionof said starboard cutter and eductor head are concurrently selectivelyengageable with the upper and lower guide rails on the starboard side ofsaid second set of spanning beams.

tor head for horizontally adjusting the starboard cutter and eductorhead upon said guide rails on the starboard side of said first andsecond set of spanning beams.

12. An apparatus for entrenching a submerged pipeline and the likewithin the bed of a body of water as defined in claim 10 wherein:

said guide rails comprise horizontally extending T- slots; and

said end elements comprise horizontally extending T-shaped fittingsoperably engageable within a corresponding guide rail T-slot.

13. An apparatus for entrenching a submerged pipeline and the likewithin the bed of a body of water as defined in claim 12 and furthercomprising:

a plurality of lock rails, one being connected to and extendinggenerally coextensive with each of said upper and lower, port andstarboard guide rails on the first set of spanning beams and the secondset of spanning beams; said lock rails each include,

a plurality of horizontally spaced locking apertures, and a locking boltoperably connected to the locking rail adjacent each of saidhorizontally spaced locking apertures; said T-shaped fittings eachinclude in a lower portion thereof a pair of horizontally spacedapertures operably spaced for alignment with said locking apertures inone of said locking rails whereby a pair of locking bolts may beselectively engageable through a corresponding pair of apertures in saidT-shaped fittings and said locking rails to maintain a desiredhorizontal position of the port and starboard cutter and eductor headswith respect to said box frame.

14. An apparatus for entrenching a submerged pipeline and the likewithin the bed of a body of water comprising:

a burying sled, including first and second pontoon skids havinggenerally mutually parallel longitudinal axes, said pontoon mergedpipeline to be entrenched, and

a box frame bridging said first and second spaced pontoon skidsincluding,

a first set of upper and lower vertically spaced horizontally extendingspanning beams connected between said first and second spaced pontoonskids and extending generally normally with respect to the longitudinalaxes of said pontoon skids, and

a second set of upper and lower vertically spaced horizontally extendingspanning beams connected between said first and second spaced pontoonskids and extending generally normally with respect to the longitudinalaxes of said pontoon skids, said second set of spanning beams extendinggenerally parallel with respect to said first set of spanning beams andbeing offset with respect thereto; and

spect to the central longitudinal axis of said second conduit segmentand generally parallel with respect to the central longitudinal axis ofsaid first conduit segment, said third conduit segment having, aplurality of jetting apertures fashioned therein,

wherein said first conduit segments of said first and second cutterheads have generally mutually parallel central longitudinal axes and areoperatively adapted to extend generally vertically on opposite sides ofa pipeline to be entrenched, and said third conduit segments of saidfirst and second cutter heads have generally mutually parallel centrallongitudinal axes and extend generally vertically beneath a pipeline tobe entrenched whereby the perpendicular distance between the generallymutually parallel longitudinal axes of said first conduit segments isgreater than the perpendicular distance between the generally mutuallyparallel longitudinal axes of said third conduit segments.

15. An apparatus for entrenching a submerged pipeline and the likewithin the bed of a body of water as defined in claim 14 and furthercomprising:

means connected to said burying sled for withdrawing particles offluidized material from adjacent said means for cutting comprising: afirst eductor head having first, second and third means connected tosaid burying sled for cutting a trench beneath a submerged pipelinewithin the bed of the body of water comprising:

a first cutter head including,

a first conduit segment having a central longitudinal axis operablypositionable generally verti- 2 cally along one side of a pipeline to beentrenched, said first conduit segment having:

a plurality of jetting apertures fashioned therein,

a second conduit segment connected at one end LII to said first conduitsegment, said second conduit segment having a central longitudinal axisextending at an angle with respect to the central longitudinal axis ofsaid first conduit segment, said second conduit segment having, aplurality of jetting apertures fashioned therein,

a third conduit segment connected at one end to the other end of saidsecond conduit segment,

conduit segments positioned adjacent to and extending generallycoextensive with said first, second and third conduit segmentsrespectively of said first cutter head, and

a second eductor head having first, second and third conduit segmentspositioned adjacent to and extending generally coextensive with saidfirst, second and third conduit segments respectively of said secondcutter head.

said third conduit segment having a central longitudinal axis extendingat an angle with respect to the central longitudinal axis of said secondconduit segment and generally parallel with respect to the centrallongitudinal axis of said first conduit segment, said third conduitsegment having, a plurality of jetting apertures fashioned therein, anda second cutter head including,

a first conduit segment having a central longitudinal axis operablypositionable generally vertically along an opposite side of a pipelineto be entrenched, said first conduit segment having, a plurality ofjetting apertures fashioned therein,

a second conduit segment connected atone end to said first conduitsegment, said second condtiit segment having a central longitudinal axisextending at an angle with respect to the cen- 6 tral longitudinal axisof said first conduit segment, said second conduit segment having,

a plurality of jetting apertures fashioned therein,

a third conduit segment connected at one end to 65 the other end of saidsecond conduit segment, said third conduit segment having a centrallongitudinal axis extending at an angle with re 16. An apparatus forentrenching a submerged pipeline and the like within the bed of a bodyof water as defined in claim 14 and further comprising:

upper and lower guide rails connected on the port side of said first setof spanning beams to said upper and lower vertically spaced spanningbeams respectively;

upper and lower guide rails connected on the starboard side of saidfirst set of spanning beams to said upper and lower vertically spacedspanning beams respectively;

upper and lower guide rails connected on the port side of said secondset of spanning beams to said upper and lower vertically spaced spanningbeams respectively; and

upper and lower guide rails connected on the starboard side of saidsecond set of spanning beams to said upper and lower vertically spacedspanning beams respectively.

17. An apparatus for entrenching a submerged pipeline and the likewithin the bed of a body of water as defined in claim 16 and furthercomprising:

a plurality of vertically spaced horizontally extending support armsextending from each of the fore and aft portions of said port andstarboard cutter and eductor heads, each one of said support arms isfitted with an end element connected thereto, and

said support arms being operably vertically spaced so that;

a pair of the plurality of support arms extending from the fore portionof said port cutter and slots; and

said end elements comprise horizontally extending T-shaped fittingsoperably engageable within a corresponding guide rail T-slot.

eductor head are selectively engageable with 19. An apparatus forentrenching a submerged pipethe upper and lower guide rails on the portside line and the like within the bed of a body of water as of saidfirst set of spanning beams, and defined in claim 18 and furthercomprising:

a pair of the plurality of support arms extending a plurality of lockrails, one being connected to and from the aft portion of said portcutter and extending generally coextensive with each of said eductorhead are concurrently selectively en- 0 upper and lower port andstarboard guide rails on gageable with the upper and lower guide railsthe first set of spanning beams and the second set on the port side ofsaid second set of spanning of spanning beams; beams, and said lockrails each include,

a pair of the plurality of support arms extending a plurality ofhorizontally spaced locking aperfrom the fore portion of said starboardcutter tures, and and eductor head are selectively engageable a lockingbolt operably connected to the locking with the upper and lower guiderails on the rail adjacent each of said horizontally spaced starboardside of said first set of spanning locking apertures; beams, and saidT-shaped fittings each include in a lower pora pair of the plurality ofsupport arms extending 20 tion thereof a pair of horizontally spacedapert'rom the aft portion of said starboard cutter tures operably spacedfor alignment with said and eductor head are concurrently selectivelylocking apertures in one of said locking rails engageable with the upperand lower guide whereby a pair of locking bolts may be selecrails on thestarboard side of said second set of tively engageable through acorresponding pair spanning beams. of apertures in said T-shapedfittings and said 18. An apparatus for entrenching a submergedpipelocking rails to maintain a desired horizontal poline and the likewithin the bed of a body of water as sition of the port and starboardcutter and educdefined in claim 17 wherein tor heads with respect tosaid box frame.

said guide rails comprise horizontally extending T-

1. An apparatus for entrenching a submerged pipeline and the like withinthe bed of a body of water comprising: a frame operable to be loweredover and transported along a submerged pipeline to be entrenched; andmeans connected to said frame for cutting a trench beneath a submergedpipeline within the bed of the body of water comprising, a first cutterhead including a first conduit segment having a central longitudinalaxis operably positionable genErally vertically along one side of apipeline to be entrenched, said first conduit segment having, aplurality of jetting apertures fashioned therein, a second conduitsegment connected at one end to said first conduit segment, said secondconduit segment having a central longitudinal axis extending at anobtuse angle with respect to the central longitudinal axis of said firstconduit segment, said second conduit segment having, a plurality ofjetting apertures fashioned therein, a third conduit segment connectedat one end to the other end of said second conduit segment, said thirdconduit segment having a central longitudinal axis extending at an anglewith respect to the central longitudinal axis of said second conduitsegment and generally parallel with respect to the central longitudinalaxis of said first conduit segment, said third conduit segment having, aplurality of jetting apertures fashioned therein, and a second cutterhead including, a first conduit segment having a central longitudinalaxis operably positionable generally vertically along an opposite sideof a pipeline to be entrenched, said first conduit segment having, aplurality of jetting apertures fashioned therein, a second conduitsegment connected at one end to said first conduit segment, said secondconduit segment having a central longitudinal axis extending at an anglewith respect to the central longitudinal axis of said first conduitsegment, said second conduit segment having, a plurality of jettingapertures fashioned therein, a third conduit segment connected at oneend to the other end of said second conduit segment, said third conduitsegment having a central longitudinal axis extending at an angle withrespect to the central longitudinal axis of said second conduit segmentand generally parallel with respect to the central longitudinal axis ofsaid first conduit segment, said third conduit segment having, aplurality of jetting apertures fashioned therein, wherein said firstconduit segments of said first and second cutter heads have generallymutually parallel central longitudinal axes and are operatively adaptedto extend generally vertically on opposite sides of a pipeline to beentrenched, and said third conduit segments of said first and secondcutter heads have generally mutually parallel central longitudinal axesand extend generally vertically beneath a pipeline to be entrenchedwhereby the perpendicular distance between the generally mutuallyparallel longitudinal axes of said first conduit segments is greaterthan the perpendicular distance between the generally mutually parallellongitudinal axes of said third conduit segments.
 2. An apparatus forentrenching a submerged pipeline and the like within the bed of a bodyof water as defined in claim 1 and further comprising: means connectedto said frame for withdrawing particles of fluidized matter fromadjacent said means for cutting comprising, a first eductor head havingfirst, second and third conduit segments positioned adjacent to andextending generally coextensive with said first, second and thirdconduit segments respectively of said first cutter head, and a secondeductor head having first, second and third conduit segments positionedadjacent to and extending generally coextensive with said first, secondand third conduit segments respectively of said second cutter head. 3.An apparatus for entrenching a submerged pipeline and the like withinthe bed of a body of water as defined in claim 2 and further comprising:means connecting said first cutter head and said first eductor head tosaid frame for independent horizontal and vertical adjustability thereofwith respect to said frame, and means connecting said second cutter headand said second eductor head to said frame for independent horizontaland vertical adjustability thereof with respect to said frame.
 4. Anapparatus for entrenching a submerged pipeline and thE like within thebed of a body of water comprising: a burying sled, including first andsecond pontoon skids having generally mutually parallel longitudinalaxes, said pontoon skids being operably spaced to straddle a submergedpipeline to be entrenched, and a box frame bridging said first andsecond spaced pontoon skids including, a first set of upper and lowervertically spaced horizontally extending spanning beams connectedbetween said first and second spaced pontoon skids and extendinggenerally normally with respect to the longitudinal axes of said pontoonskids, and a second set of upper and lower vertically spacedhorizontally extending spanning beams connected between said first andsecond spaced pontoon skids and extending generally normally withrespect to the longitudinal axes of said pontoon skids, said second setof spanning beams extending generally parallel with respect to saidfirst set of spanning beams and being offset with respect thereto, acutter and eductor head operably mounted between said first set ofspanning beams and said second set of spanning beams on the port side ofsaid burying sled for independent vertical and horizontal adjustmentwith respect thereto; and a cutter and eductor head operably mountedbetween said first set of spanning beams and said second set of spanningbeams on the starboard side of said burying sled for independentvertical and horizontal adjustment with respect thereto.
 5. An apparatusfor entrenching a submerged pipeline and the like within the bed of abody of water as defined in claim 4 wherein said first and secondpontoon skids include: first and second longitudinally extending platemembers having an arc shaped cross-sectional configuration connected injuxtaposition to a bottom portion of said first and second pontoon skidsrespectively.
 6. An apparatus for entrenching a submerged pipeline andthe like within the bed of a body of water as defined in claim 4 andfurther comprising: upper and lower guide rails connected on the portside of said first set of spanning beams to said upper and lowervertically spaced spanning beams respectively; upper and lower guiderails connected on the starboard side of said first set of spanningbeams to said upper and lower vertically spaced spanning beamsrespectively; upper and lower guide rails connected on the port side ofsaid second set of spanning beams to said upper and lower verticallyspaced spanning beams respectively; and upper and lower guide railsconnected on the starboard side of said second set of spanning beams tosaid upper and lower vertically spaced spanning beams respectively. 7.An apparatus for entrenching a submerged pipeline and the like withinthe bed of a body of water as defined in claim 6 wherein said guiderails include: generally horizontally extending T-shaped slots.
 8. Anapparatus for entrenching a submerged pipeline and the like within thebed of a body of water as defined in claim 6 and further comprising: aplurality of lock rails, one being connected to and extending generallycoextensive with each of said upper and lower, port and starboard guiderails on said first set of spanning beams and said second set ofspanning beams.
 9. An apparatus for entrenching a submerged pipeline andthe like within the bed of a body of water as defined in claim 8 whereineach of said lock rails includes: a plurality of horizontally spacedlocking apertures; and a locking bolt operably connected to the lockingrail adjacent each of said horizontally spaced locking apertures.
 10. Anapparatus for entrenching a submerged pipeline and the like within thebed of a body of water as defined in claim 6 and further comprising: aplurality of vertically spaced horizontally extending cantilever supportarms extending from each of the fore and aft portions of said port andstarboard cutter and eductor heads, each one of said support arms isfitted with aN end element and connected thereto,and said support armsbeing operably vertically spaced so that, a pair of the plurality ofsupport arms extending from the fore portion of said port cutter andeductor head are selectively engageable with the upper and lower guiderails on the port side of said first set of spanning beams, and a pairof the plurality of support arms extending from the aft portion of saidport cutter and eductor head are concurrently selectively engageablewith the upper and lower guide rails on the port side of said second setof spanning beams, and a pair of the plurality of support arms extendingfrom the fore portion of said starboard cutter and eductor head areselectively engageable with the upper and lower guide rails on thestarboard side of said first set of spanning beams, and a pair of theplurality of support arms extending from the aft portion of saidstarboard cutter and eductor head are concurrently selectivelyengageable with the upper and lower guide rails on the starboard side ofsaid second set of spanning beams.
 11. An apparatus for entrenching asubmerged pipeline and the like within the bed of a body of water asdefined in claim 10 and further comprising: a port adjustment motorconnected between said box frame and said port cutter and eductor headfor horizontally adjusting said cutter and eductor head upon said guiderails on the port side of said first and second set of spanning beams;and a starboard adjustment motor connected between said box frame andsaid starboard cutter and eductor head for horizontally adjusting thestarboard cutter and eductor head upon said guide rails on the starboardside of said first and second set of spanning beams.
 12. An apparatusfor entrenching a submerged pipeline and the like within the bed of abody of water as defined in claim 10 wherein: said guide rails comprisehorizontally extending T-slots; and said end elements comprisehorizontally extending T-shaped fittings operably engageable within acorresponding guide rail T-slot.
 13. An apparatus for entrenching asubmerged pipeline and the like within the bed of a body of water asdefined in claim 12 and further comprising: a plurality of lock rails,one being connected to and extending generally coextensive with each ofsaid upper and lower, port and starboard guide rails on the first set ofspanning beams and the second set of spanning beams; said lock railseach include, a plurality of horizontally spaced locking apertures, anda locking bolt operably connected to the locking rail adjacent each ofsaid horizontally spaced locking apertures; said T-shaped fittings eachinclude in a lower portion thereof a pair of horizontally spacedapertures operably spaced for alignment with said locking apertures inone of said locking rails whereby a pair of locking bolts may beselectively engageable through a corresponding pair of apertures in saidT-shaped fittings and said locking rails to maintain a desiredhorizontal position of the port and starboard cutter and eductor headswith respect to said box frame.
 14. An apparatus for entrenching asubmerged pipeline and the like within the bed of a body of watercomprising: a burying sled, including first and second pontoon skidshaving generally mutually parallel longitudinal axes, said pontoon skidsbeing operably spaced to straddle a submerged pipeline to be entrenched,and a box frame bridging said first and second spaced pontoon skidsincluding, a first set of upper and lower vertically spaced horizontallyextending spanning beams connected between said first and second spacedpontoon skids and extending generally normally with respect to thelongitudinal axes of said pontoon skids, and a second set of upper andlower vertically spaced horizontally extending spanning beams connectedbetween said first and second spaced pontoon skids and extendinggenerally normally with respect to the loNgitudinal axes of said pontoonskids, said second set of spanning beams extending generally parallelwith respect to said first set of spanning beams and being offset withrespect thereto; and means connected to said burying sled for cutting atrench beneath a submerged pipeline within the bed of the body of watercomprising: a first cutter head including, a first conduit segmenthaving a central longitudinal axis operably positionable generallyvertically along one side of a pipeline to be entrenched, said firstconduit segment having: a plurality of jetting apertures fashionedtherein, a second conduit segment connected at one end to said firstconduit segment, said second conduit segment having a centrallongitudinal axis extending at an angle with respect to the centrallongitudinal axis of said first conduit segment, said second conduitsegment having, a plurality of jetting apertures fashioned therein, athird conduit segment connected at one end to the other end of saidsecond conduit segment, said third conduit segment having a centrallongitudinal axis extending at an angle with respect to the centrallongitudinal axis of said second conduit segment and generally parallelwith respect to the central longitudinal axis of said first conduitsegment, said third conduit segment having, a plurality of jettingapertures fashioned therein, and a second cutter head including, a firstconduit segment having a central longitudinal axis operably positionablegenerally vertically along an opposite side of a pipeline to beentrenched, said first conduit segment having, a plurality of jettingapertures fashioned therein, a second conduit segment connected at oneend to said first conduit segment, said second conduit segment having acentral longitudinal axis extending at an angle with respect to thecentral longitudinal axis of said first conduit segment, said secondconduit segment having, a plurality of jetting apertures fashionedtherein, a third conduit segment connected at one end to the other endof said second conduit segment, said third conduit segment having acentral longitudinal axis extending at an angle with respect to thecentral longitudinal axis of said second conduit segment and generallyparallel with respect to the central longitudinal axis of said firstconduit segment, said third conduit segment having, a plurality ofjetting apertures fashioned therein, wherein said first conduit segmentsof said first and second cutter heads have generally mutually parallelcentral longitudinal axes and are operatively adapted to extendgenerally vertically on opposite sides of a pipeline to be entrenched,and said third conduit segments of said first and second cutter headshave generally mutually parallel central longitudinal axes and extendgenerally vertically beneath a pipeline to be entrenched whereby theperpendicular distance between the generally mutually parallellongitudinal axes of said first conduit segments is greater than theperpendicular distance between the generally mutually parallellongitudinal axes of said third conduit segments.
 15. An apparatus forentrenching a submerged pipeline and the like within the bed of a bodyof water as defined in claim 14 and further comprising: means connectedto said burying sled for withdrawing particles of fluidized materialfrom adjacent said means for cutting comprising: a first eductor headhaving first, second and third conduit segments positioned adjacent toand extending generally coextensive with said first, second and thirdconduit segments respectively of said first cutter head, and a secondeductor head having first, second and third conduit segments positionedadjacent to and extending generally coextensive with said first, secondand third conduit segments respectively of said second cutter head. 16.An apparatus for entrenching a submerged pipeline and the like withinthe bed of a body of watEr as defined in claim 14 and furthercomprising: upper and lower guide rails connected on the port side ofsaid first set of spanning beams to said upper and lower verticallyspaced spanning beams respectively; upper and lower guide railsconnected on the starboard side of said first set of spanning beams tosaid upper and lower vertically spaced spanning beams respectively;upper and lower guide rails connected on the port side of said secondset of spanning beams to said upper and lower vertically spaced spanningbeams respectively; and upper and lower guide rails connected on thestarboard side of said second set of spanning beams to said upper andlower vertically spaced spanning beams respectively.
 17. An apparatusfor entrenching a submerged pipeline and the like within the bed of abody of water as defined in claim 16 and further comprising: a pluralityof vertically spaced horizontally extending support arms extending fromeach of the fore and aft portions of said port and starboard cutter andeductor heads, each one of said support arms is fitted with an endelement connected thereto, and said support arms being operablyvertically spaced so that; a pair of the plurality of support armsextending from the fore portion of said port cutter and eductor head areselectively engageable with the upper and lower guide rails on the portside of said first set of spanning beams, and a pair of the plurality ofsupport arms extending from the aft portion of said port cutter andeductor head are concurrently selectively engageable with the upper andlower guide rails on the port side of said second set of spanning beams,and a pair of the plurality of support arms extending from the foreportion of said starboard cutter and eductor head are selectivelyengageable with the upper and lower guide rails on the starboard side ofsaid first set of spanning beams, and a pair of the plurality of supportarms extending from the aft portion of said starboard cutter and eductorhead are concurrently selectively engageable with the upper and lowerguide rails on the starboard side of said second set of spanning beams.18. An apparatus for entrenching a submerged pipeline and the likewithin the bed of a body of water as defined in claim 17 wherein : saidguide rails comprise horizontally extending T-slots; and said endelements comprise horizontally extending T-shaped fittings operablyengageable within a corresponding guide rail T-slot.
 19. An apparatusfor entrenching a submerged pipeline and the like within the bed of abody of water as defined in claim 18 and further comprising: a pluralityof lock rails, one being connected to and extending generallycoextensive with each of said upper and lower port and starboard guiderails on the first set of spanning beams and the second set of spanningbeams; said lock rails each include, a plurality of horizontally spacedlocking apertures, and a locking bolt operably connected to the lockingrail adjacent each of said horizontally spaced locking apertures; saidT-shaped fittings each include in a lower portion thereof a pair ofhorizontally spaced apertures operably spaced for alignment with saidlocking apertures in one of said locking rails whereby a pair of lockingbolts may be selectively engageable through a corresponding pair ofapertures in said T-shaped fittings and said locking rails to maintain adesired horizontal position of the port and starboard cutter and eductorheads with respect to said box frame.